A. Field of the Invention
The present invention relates to a damper mechanism, and in particular to a damper mechanism which transmits a torque from an input rotary member to an output rotary member and simultaneously dampens a vibration during torque transmission.
B. Description of the Background Art
In general, a damper mechanism transmits a torque from an input rotary member to an output rotary member and simultaneously dampens a vibration which may be transmitted from the input rotary member to the output rotary member. A lockup clutch damper mechanism (which will also be referred to as a "lockup dampery mechanism" hereinafter) disposed in a torque converter is one such damper mechanism.
Generally, the torque converter is internally provided with three types of vane wheels, an impeller, a turbine and a stator), and is operable to transmit a torque through a working fluid in the torque converter. The impeller is fixed to a front cover which coupled to the input rotary member for rotation therewith, and transmits torque to the turbine through the working fluid, which flows from the impeller to the turbine and then through the stator back to the impeller. The torque is then transmitted to the output rotary member which is coupled to the turbine.
The lockup damper mechanism is disposed between the turbine and the front cover for selectively mechanically coupling the front cover and the turbine together and thereby directly transmitting the torque from the front cover to the output rotary member.
Typically, the lockup damper mechanism has a piston which can be selectively pressed against the front cover, a retaining plate fixed to the piston, torsion springs supported by the retaining plate through spring seats, and a driven plate elastically coupled in the rotating direction of the damper mechanism to the piston by the torsion springs. The driven plate is fixed to the turbine. The spring seats support opposing ends of the torsion springs, are contactable with the retaining plate, and restrict the movement of the torsion springs in the rotating direction.
When the lockup damper mechanism operates, the torque is transmitted from the front cover to the piston, and then is transmitted through the torsion springs to the turbine. The lockup damper mechanism transmits the torque, and simultaneously dampens vibrations as a result of the torsion springs being compressed and then expanding between the driven plate and the retaining plate.
The torsion springs are restrained from radially outward movement by bent outer peripheral portions of the retaining plate, which will be referred to as outer bent portions hereinafter.
When the lockup damper mechanism rotates, centrifugal forces act on the torsion springs and other components, so that the torsion springs and spring seats are urged against the outer bent portions. When the torsion springs compress and expand with their spring seats urged against the outer bent portions, the damper characteristics change due to frictional resistance produced between the spring seats and the outer bent portions. As a result, it is necessary to employ the outer bent portions having a sufficiently large thickness because the friction caused by movement of the spring seats causes wear of the outer peripheral portions thereof. However, it is desired to reduce the thickness in order to reduce the weight of the lockup damper mechanism.